The JET nuclear fusion reactor in Oxfordshire, UK, set many records over its 40 years of operation, pushing forward our understanding of how to spark and contain reactions of the type normally only found within the heart of a star. Although it has now reached the end of its life, it will break records once more as the team behind the experiment attempt something that has never been done before: recycling a fusion reactor.
“We want to repurpose the assets as much as possible – there’s well over a billion’s worth of equipment here – [and] use it again, as much as we can, for UK science,” says , the head of the UK Atomic Energy Authority (UKAEA). “We’re going to learn a whole load just going through that process.”
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No tokamak reactor – the doughnut-shaped fusion device that is one of a clutch of designs currently being worked on around the world – has ever been carefully deconstructed in this way. The closest attempt was the US , which was simply disposed of like nuclear waste at the end of its life – they “chopped it up, grouted it, buried it”, says Chapman.
Standing in the cavernous room that houses the defunct reactor, I can hear it still emitting a loud hum, but after 105,929 attempts at ignition, this machine will never fire again. Instead, the noises are from the dense layers of infrastructure that obscure the reactor’s plasma vessel, cooling its componentsĚýand keeping fresh air passing through it, scrubbing any contaminants before it is released to the room outside.
Dozens of researchers have climbed within JET’s 100-cubic-metre vessel over the decades, having to squeeze through a tiny port around 40 centimetres by 80 centimetres – something that I am told takes a certain technique of twisting the shoulders and isn’t a job for the claustrophobic.
But Gary Hermon, who works on the robotic arms that maintained JET and will now be used to decommission it, says no human will ever be allowed inside again. That is because final, record-breaking experiments “turned the power up to 11” and left the interior more contaminated than ever before, he says. “It’s become a very hostile environment. Why send humans in if you can use technology?”
Instead, scientists will have to make do with robotic arms, which date back to the 1980s, and show signs of their age. They will operate them remotely from a control room, 5 minutes’ walk from the reactor itself. This is a much safer and more comfortable job, but also a much trickier one. The robots themselves have to perform a similar contortion to enter the same small port, while also wearing a disposable plastic gown that shields them from radioactive contamination (see top image).
Despite shutting down, the site will remain a hive of activity. During operation, there were around 600 engineers and scientists working on JET, and during the decommissioning, there will still be 200. The rest will stay in fusion research, says Chapman, moving to other projects under UKAEA control. Their work may come too late to inform the design of the machine’s replacement, ITER, currently being built in France, but it will help steer the design of the UK’s Spherical Tokamak for Energy Production (STEP) reactor that is hoped to be up and running by 2035.
Current and former JET workers touring the reactor with me have some incredible, if scary, stories to tell. Elena Righi, head of Euratom Research at the European Commission, who worked for JET for seven years from 1990, recalls working overnight and hearing a loud bang from inside the reactor. She was certain that she would be fired for damaging the machine, but, in the morning, nothing untoward was found. “This machine was built to outlast us,” she says. Another worker recalls the time computer instructions were accidentally run backwards, pushing an experiment far harder than expected, but revealing that the plasma vessel could take it.Ěý
Yet despite that solid construction, JET’s time as a useful experiment eventually ran out. As parts of the reactor are removed, they will be carefully inspected for clues as to how they became contaminated, where retrievable fuel is located and how components degraded – all vital information that will help in the operation and dismantling of future reactors.
Various diagnostic systems, cameras, heating systems and vacuum chambers will be stripped and shipped to other fusion projects, both those run by UKAEA and elsewhere. One of JET’s large flywheels, which helped power experiments, will go to the National Grid to help stabilise the UK’s power supply. Other parts – yet to be determined – will be made available to UK museums.
Despite the extraordinary nuclear reactions that took place inside JET over 40 years, the final amount of radioactive waste left over after decommissioning will fit in just two or three containers each around the size of a small car. Most of the fuel embedded in components will be reclaimed, packaged up and stored for future experiments, says Chapman. JET’s legacy looks set to continue as researchers attempt to harness the awesome potential of nuclear fusion.
